The error message is telling you that something is wrong with the file mentioned in the error message, which is the settings file associated with JSON files. Generally speaking in order to stop the message from opening every time you need to either fix the file to not be broken, or remove it entirely.
If you use Preferences > Browse Packages
from the menu, that will show you the contents of the Packages
folder, and from there you go into User
folder and then open the JSON.sublime-settings
file to fix it. The :1:1
on the end of the file name is telling you that the error is occurring on Line 1, Column 1 (i.e. the start of the file).
All sublime-settings
files need to be valid JSON; it’s hard to say what the problem might be without seeing what the contents of your file looks like, but the very first character should be {
at the very least, which it sounds like it’s not. A common problem is to accidentally paste a setting into the file in the wrong place, for example.